In hermetic compressors for commercial and domestic refrigeration, an important factor for the correct operation thereof is the adequate lubrication of the components that move relatively to each other. The difficulty in obtaining such lubrication is associated to the fact that the oil must flow upwardly to lubricate said parts with relative movement. Among the known solutions for obtaining such lubrication, there is one that uses the principles of centrifugal force and that of mechanical drag.
In one of these solutions, which is used both in the linear compressors and the reciprocating compressors, in order to supply oil to the piston/cylinder assembly, it is necessary to make the gas flow, from the compressor suction and which generates a small pressure differential in relation to the oil sump, draw said oil through a capillary tube, mixing it with the gas drawn by the compressor, said mixture being admitted to the inside of the cylinder by the suction valve, so that the oil lubricates the contact parts between the piston and the cylinder. As a function of the low gas flow that is drawn by the compressor in certain situations, this construction is not always efficient.
In other known construction (WO97/01033), the compression and suction forces of the piston are used to displace the lubricant oil from the oil sump formed in a lower portion of the compressor shell, to an upper reservoir formed around the cylinder of said compressor, through a capillary tube, said upper reservoir being connected to the inside of the cylinder by a plurality of orifices formed in the wall thereof and which serve for admitting oil to the interior of the piston-cylinder gap when the piston is performing the suction movement, and for discharging said oil when the piston is performing the reverse movement. The oil is discharged to a set of channels formed in the valve plate of the compressor, further increasing the suction flow and making said oil re-enter into the cylinder.
Other known solution (WO 97/01032) uses a resonant mass that reciprocates inside a cavity formed on the external side of the cylinder, said resonant mass drawing oil from the sump while moving in one direction, said oil passing through a tube and through a check valve that allows only the admission of oil into said cavity, the latter being connected to the inside of the cylinder by a plurality of orifices formed in the wall thereof. The oil of said cavity is expelled when the resonant mass moves in the other direction and passes through a check valve that allows only the discharge of oil from said cavity. Although being functional, this solution is difficult to manufacture and its construction has many components.
In the above cited patent application PI0004286 of the same applicant, there is disclosed an oil pump means that is driven by the reciprocating movement of either the piston or the cylinder, said oil pump means being formed by a plunger, inside which is provided a movable seal that is displaceable between a closing position, in which it is seated against a valve seat located adjacent to an oil inlet orifice defined in the body of the oil pump means, and an opening position, in which said seal is moved away from the valve seat, said positions being axially spaced from each other, a maximum spacing being obtained, for example, when the seal reaches a stop provided inside the body of said oil pump means. When the oil pump moves in a determined direction and sense (as illustrated in FIG. 1), the seal is displaced towards the stop, allowing said oil to enter through the inlet orifice and pushing the column of oil in the opposite direction to the movement of said oil pump means. When the oil pump moves in the opposite direction to that described above, as indicated in FIG. 2, the seal moves towards the valve seat, blocking the entrance of oil to the inside of the body of the oil pump means and avoiding the admitted oil from coming out through the inlet orifice. Thus, with the continuous reciprocation of the oil pump means, the oil is continuously admitted and impelled through the body of the oil pump means towards the movable parts of the compressor to be lubricated.
In the linear compressors, said oil pump means is mounted in the same direction of movement as the resonant assembly. Such movement makes the mechanical assembly, which is placed on a suspension system, have a reciprocating movement to drive the oil pump means. The above solution uses the reciprocation of one of the resonant assembly and non-resonant assembly of the compressor to impel, by inertia, the oil supply to the oil pump means and from the latter to the movable parts of the compressor requiring lubrication.
Nevertheless, the reciprocating movements in the compressors driven by a linear motor are known to generally have great amplitudes.
Moreover, in the particular construction of the oil pump means of said patent application PI0004286.2, great amplitudes of oscillation lead to the occurrence of strong shocks of the seal of said oil pump means against the stop to the displacement thereof and against the valve seat of the oil pump means, causing damage to these components with the continuous operation of the compressor, which impairs the reliability of said compressor and increases the levels of noise during its operation.